Slip Trace Analysis Research Articles

An investigation of slip and twinning behavior of a zirconium alloy during plastic deformation based on in-situ SEM-EBSD

In this study, a combination of in-situ scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) was employed to investigate the tensile deformation behavior of Zr-4 alloy at room temperature. Slip trace analysis shows that the prismatic <a> slip is activated at the initial stage of deformation, while other slip modes are also activated with strain increasing. In-Grain Misorientation Axis (IGMA) analysis demonstrates a significant increase in the probability of non-prismatic slip in non-basal textured grains. In terms of twinning behavior, when the twin nucleation critical stress is lower than the global applied stress, slip-independent twins could form at lower strain. When the twin nucleation critical stress is higher than the global applied stress, slip-assisted twins could form due to the high local strain caused by the adjacent grains.

Quasi-in-situ observation on high-strain-rate deformation of Ti-xO(x=0.2, 0.4) polycrystals

Under high strain rates, the effects of aluminum and vanadium on the deformation mechanisms of pure titanium have been revealed. However, the effect of oxygen, a prevalent interstitial element, remains less understood. In this study, we conducted dynamic uniaxial compressive loading on Ti-xO (x = 0.2, 0.4 wt%) polycrystals along the rolling direction (RD) using a split Hopkinson pressure bar (SHPB). Deformation mechanisms were analyzed via quasi-in-situ electron backscatter diffraction (EBSD) and slip trace analysis. The findings indicate that twinning and dislocation slip are significant in the Ti-0.2O polycrystal, with dislocation slip predominating in the Ti-0.4O polycrystal. Both polycrystals primarily activate {101‾2} tensile twins; however, twin nucleation and growth are markedly reduced in the Ti-0.4O polycrystal, a phenomenon associated with enhanced stacking fault energy (SFE) and oxygen segregation {101‾2} tensile twin boundaries. Unlike in quasi-static conditions, prismatic <a> slip is more probable in the Ti-0.4O polycrystal, while basal <a> slip, first-order pyramidal <a> slip, first-order pyramidal <c+a> slip, and second-order pyramidal <c+a> slip are inhibited to varying extents. These variations are attributed to increases in the ∣b<c+a>∣/∣b<a>∣ ratio, CRSSBasal<a>/CRSSPrismatic<a> ratio, and CRSSFirst-order pyramidal<a>/CRSSPrismatic<a> ratio with higher oxygen content. The Burgers vector is identified as more critical than the critical resolved shear stress (CRSS). Additionally, cross-slip between the <c+a> slip systems occurs in both polycrystals, facilitated by the complex core structure of the <c+a>-type dislocation. However, enhanced oxygen-dislocation interactions in the Ti-0.4O polycrystal result in reduced cross-slip planes.

Unveiling the mechanical anisotropy and related deformation mechanisms of heterostructured Mg alloy laminate with unique texture feature

In this study, a well-bonded AZ31/ZK60/AZ31 sandwich-structured laminate was prepared using extrusion. Microstructural heterogeneities in grain size, precipitate phases, and texture were evident between the constituent layers. Tensile testing revealed significant mechanical anisotropy in the laminates along the extrusion direction (ED), transverse direction (TD), and 45° directions, with the 45° direction samples exhibiting the highest tensile ductility, while ED and TD samples showed similar high strength. In-situ electron backscatter diffraction and slip trace analysis indicated that the heterogeneities in grain size and precipitates had minimal influence on the mechanical anisotropy of the laminates. Instead, texture emerged as the primary influencing factor, as it affected the initiation difficulty of basal slip and extension twinning mechanisms in various directions, thereby influencing the deformation coordination between the successive layers and resulting in varied mechanical responses in different directions.

Ascertaining the deformation accommodation of a novel Ti-652 alloy by tracking the evolution of slip traces and lattice strain

The exploration of slip modes in metallic materials during deformation has been long suffered from either insufficient statistical accuracy of slip trace analysis or limited spatial resolution by X-ray diffraction. In this work, a combination of slip trace analysis based on in-situ Electron Backscatter Diffraction (EBSD) and lattice strain analysis supported by in-situ Synchrotron Radiation High-Energy X-ray Diffraction (SR-HEXRD) was employed to determine the deformation accommodation mechanisms of a new developed Ti-6Al-5Mo-2Sn-0.3Si-0.5 V (Ti-652) alloy. Different from conventional cases, it was surprisingly found that pyramidal (101̅1)α slip is easier to be initiated than prismatic (101̅0)α within α grains, resulting in the dominant slip modes evolving from prismatic <a> to pyramidal I <c+a>. In addition, in-situ EBSD results show that slip can transfer across grain boundary (GB) in counterintuitive situations with low geometric compatibility factor m′ of 0.5, or with GB misorientations in the range of θ≥24.5°, which are contractive to the slip transfer criterion in hcp structures. Further detailed crystallographic analysis revealed that specific slip transferred across GBs with 24.5°≤θ≤60° because of high Schmid Factor (SF) values, while with θ>60° slip transfer occurred by activating another slip systems. The accumulation of multi-mode slip dislocations induced by deformation accommodation with different phases was suggested to promote the formation of sub-GBs within the deformed parent grain. These findings provide insights of the slip behaviors and property tailoring in Ti alloys.

Fatigue mechanisms at 450°C of a highly twined (>70%) and HIP-densified IN718 superalloy additively manufactured by laser beam powder bed fusion

Fatigue resistance at elevated temperatures is crucial for certifying aerospace structures additively manufactured by the laser beam powder bed fusion (PBF-LB) method with IN718 superalloy. This study employed a multi-step, supersolvus heat treatment process with hot isostatic pressing (HIP), called RHSA, to minimize pores and brittle phases. Stress intensity factor (△K) calculations using data from X-ray computed tomography and shape factors referencing finite element analysis (FEA) studies confirmed the suppression of △K below the threshold of conventional IN718 (∼5 MPa√m), shifting fatigue behavior to grain-structure-dominated. Despite a very high twin boundary (TB) fraction (>70%), fatigue tests at 450°C and R = 0.1 demonstrated low scatter. Slip trace analysis and high-resolution electron backscatter diffraction (EBSD) revealed that TB-induced strain concentration became prominent only at high △K, causing cracking at 45⁰ to the loading direction. The randomly oriented TBs with higher angles (60⁰) compared to high-angle grain boundaries (HAGBs) (30–40⁰) likely enhanced slip resistance and provided a net strengthening effect, which can explain the lower-than-average TB% along fracture paths. These insights suggest that a high TB fraction is not detrimental if fatigue stress is not excessive, alleviating concerns about annealing twins during defect minimization in AM IN718, allowing novel processes to improve fatigue resistance in PBF-LB IN718.

The Effect of Rolling Reduction on the Microstructure Evolution and Slip Behavior of Ta-10W Alloy during Cold Rolling Process

In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy.

In-situ deformation inhomogeneity and damage evolution of mixed-grain structure with tempered sorbite/bainite in Fe–Cr–Mo–Mn steel

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power.

Crystallographic micro-mechanism of faceted crack initiation in near-α titanium alloy Ti6321 under room-temperature fatigue and dwell fatigue loadings

Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect, and it is not completely understood yet. This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms. The study demonstrated that the faceted primary α nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests. Slip trace analysis revealed that faceted cracking occurred at (0001) basal plane with the maximum Schmid factor value through a special cracking mode referred to as (0001) twist boundary cracking. Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations, which well identify candidates for (0001) twist boundary crack nucleation. It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface (0001) twist-boundary crack initiation, and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking. Based on this, phenomenological models are proposed to explain the surface (0001) twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.

Quasi In Situ Study on the Slipping Behavior and Residual Stress of Copper Strip

The preparation method of integrated circuit lead frames has transitioned from stamping to etching, rendering them more sensitive to residual stress. Consequently, the dimensional deviations caused by residual stress become more pronounced, necessitating a thorough investigation into the copper strip processing process, particularly considering the high-precision requirements of the lead frame. A quasi in situ method was employed to monitor the deformation process, and quantitative analyses and graphical reconstructions of the residual stress were conducted. The results indicated that the orientation evolution did not exhibit a significant correlation with grain size or grain aspect ratio. However, the stored energy of the different grains was related to their orientations. Further analysis of slip traces revealed that single or multiple slipping may be activated in grain subdivisions, and the Schmid factor difference ratio (SFDR) value proved to be an effective tool for analyzing this deformation mode. An even more interesting finding was that the deformation mode directly affected the residual stress distribution in local regions. The relationship between residual stress, Schmid factor, and SFDR was further analyzed, and a clear correlation between SFDR and residual stress was found in this study.

Quantitative investigation on the deformation modes and cracking behavior during cyclic torsional loading of extruded pure Mg and Mg‐3Y alloy

AbstractThis study explores the effect of adding 3 wt.% Y to pure magnesium (Mg) on its mechanical behavior under cyclic torsional loadings at room temperature. The research examines deformation and cracking modes in both pure Mg and Mg‐3Y samples. Deformation modes are monitored using quasi‐in‐situ EBSD observations coupled with slip trace analysis. The findings reveal that basal slip dominates the cyclic deformation throughout the fatigue life of the pure Mg sample, while both basal and pyramidal slip dominate the cyclic deformation in the Mg‐3Y sample. Intergranular cracking is the primary cracking mode for both samples under cyclic torsional loadings. Basal and pyramidal slip persistent slip band (PSB) cracking serves as a primary transgranular cracking mode in the pure Mg and Mg‐3Y samples, respectively. The study also investigates the underlying mechanism governing the activity of various deformation modes, cracking modes, and mechanical behavior.

The discrepancy in basal slip hardening rates of cast and extruded Mg-Y-Zr alloys

The differences in the deformation mechanisms during uniaxial tension of cast and extruded Mg–2Y-0.5Zr (wt%) alloys have been investigated by using EBSD-based slip trace analysis and VPSC simulation methods, and a novel method for counting the activity of slip/twinning using grain area has been proposed. Slip trace analysis reveals that enhanced ductility and reduced tensile-compressive asymmetry observed in the Mg–2Y-0.5Zr (wt%) alloy can be attributed to the addition of the Y element, which modified the texture, and promoted pyramidal <c + a> slip and suppressed prismatic <a> slip. The extruded alloy exhibits a distinctive pseudo-fiber bimodal microstructure, which contributes to its superior ductility. The VPSC results indicate that the CRSSnon-basal/CRSSbasal ratio of the extruded alloys decreases, whereas the CRSStwinning/CRSSbasal ratio increases, which is attributed to the different effects of the grain refinement on the different deformation modes. In addition, both the VPSC results and the slip trace analysis results indicate that the extruded alloy exhibits reduced non-basal slip activity compared to the cast alloy at similar strain levels. The work-hardening rate curves and VPSC parameters give a reasonable explanation that the key to the increase in the ductility of Mg–Y–Zr alloys after extrusion is the decrease in the basal hardening rate rather than the non-basal slip activity. The refinement of grain size leads to a significant decrease in basal slip hardening rate, primarily due to the decrease in the additional hardening effect caused by tensile twinning and the generation of an additional GBS mechanism in the pseudo fiber microstructure.

Effects of grain size and temperature on slip and twinning activity in a magnesium-rare earth alloy

Understanding the deformation mechanisms in magnesium alloys is critical to develop the next-generation high-performance magnesium alloys. In this work, the effects of grain size and temperature on slip and twinning activities in WE43 magnesium-rare earth alloy were investigated with the quasi-in-situ electron backscattering diffraction method and slip trace analysis. Compression tests were conducted for the samples with three different grain sizes at room temperature (RT) and liquid nitrogen temperature (LNT), respectively. More pyramidal slips were activated in the fine-grained sample to accommodate the plastic strain instead of more twins generated in the coarse-grained sample, which contributed to its higher strain to failure and strain hardening rate. Numerous individual twins with thin structures formed in the fine-grained sample, while thick twins were observed in the coarse-grained sample. The numerous thin twins and high activities of pyramidal slips in the fine-grained sample would be attributed to the high kernel average misorientation (KAM) value and local stress concentration around grain boundaries. Regarding temperature effects, more thin twins and twin-twin interactions were observed at LNT than at RT, and the KAM value was high around these twin boundaries, which contributed to enhancing the flow stress but reducing the strain to failure at LNT.

The effect of precipitates on low-cycle fatigue behavior of WE54 magnesium alloys under stress-controlled mode

The precipitates have a significant influence on fatigue behavior in magnesium (Mg) alloy. In this work, the effects of precipitates on deformation mode, cracking mode and mechanical behavior during low-cycle fatigue under stress-controlled mode in WE54 Mg alloy at room temperature (RT) was analyzed quantitively and statistically via quasi-in-situ electron backscattered diffraction (EBSD), slip trace analysis, coupled with transmission electron microscopy (TEM). The results reveal that precipitates promoted the activation of pyramidal < c + a > dislocation slip and suppressed the activation of tension twinning in the T6 alloy. In the T4 alloy, persistent slip band (PSB) induced cracking together with intergranular cracking dominated fatigue damage, while intergranular cracking was the primary cracking mode in the T6 alloy. The obvious cyclic hardening behavior of the T4 alloy was attributed to dynamic precipitation, whereas suppressed dynamic precipitation, restrained multiplication of dislocations, together with the appearance of PFZ generated the marginal cyclic hardening behavior in the T6 alloy. Both the T4 and T6 alloys exhibited ratcheting behavior, and precipitates suppressed ratcheting deformation in the T6 alloy. Moreover, the underlying mechanism for the higher fatigue resistance in the T6 alloy was also discussed.

Investigation of slip systems activity and grain boundary sliding in fine-grained superplastic zinc alloy

Zn alloys are desirable candidates for biodegradable materials due to their great biocompatibility and sufficient mechanical properties. Nevertheless, the most popular strengthening method by grain refinement after cold processing is usually ineffective in Zn alloys. Besides highly anisotropic deformation through a dislocation slip, grain boundary sliding (GBS) plays an important role in total deformation in fine-grained Zn alloys at room temperature (RT). Herein, Zn–0.5Cu (wt. %) alloy is fabricated by RT equal channel angular pressing, and its deformation mechanisms in tension were systematically analyzed at strain rates from 10–4 s−1 to 100 s−1. GBS contribution in total deformation was measured using surface markers and atomic force microscopy. In addition, dislocation slip activity was evaluated via electron-backscattered diffraction-based slip trace analysis. As a result, investigated alloy presents the GBS contribution in a total deformation at RT from 35% at the strain rate 100 s−1 to 70% at 10–4 s−1. Simultaneously, the number of slip-deformed grains decreased from 97.5% to 8%. Moreover, the basal slip system was dominant at all strain rates, while the prismatic and the pyramidal < c + a > slip systems were activated at the higher strain rates. The results presented here for the first time clearly show the complexity of deformation mechanisms in fine-grained Zn–0.5Cu, at significantly different strain rate conditions.

Deformation behavior and mechanism of p-type (Bi,Sb)2Te3 alloy during three-point bending test at room temperature

In order to improve the machining process to engineer microstructure and defect types so as to further enhance the thermoelectric properties, it is desirable to understand the deformation behavior and mechanism of polycrystalline Bi2Te3 alloys. This work investigated the deformation behavior and mechanism of (Bi,Sb)2Te3 alloy during three-point bending tests using electron backscatter diffraction (EBSD). Results indicated that both dislocation slip and twinning occurred during the bending tests. The twins with the twin orientation relationship of (0001)M//(0001)T were observed. In addition, the nano-grains extruded the coarse grains in such a way that coarse grains assumed an orientation vulnerable to fracture along the basal planes. Slip trace analysis revealed that 13<112¯0> dislocation slipping on basal planes broke the Van der Waals bonds between the basal planes which eventually led grains to fracture. Additionally, a novel model was introduced that first incorporated the bending moment diagram in order to deduce the deformation process.

Towards strength-ductility synergy in a weak-textured Mg–3Y extruded sheet via pre-twinning and annealing

Mg-RE (magnesium-rare earth) binary alloys, such as Mg–Y alloys, usually exhibit weakened texture and excellent plasticity compared with traditional RE-free Mg alloys. However, the weakened texture could lead to a significant decrease in the strength of Mg-RE binary alloys. In this work, the weak-textured Mg–3Y (wt. %) extruded sheet displayed good strength-ductility synergy with a 41% increase in the yield strength and a good ductility similar to the initial sheet via simple pre-twinning and annealing treatment (PT). After PT, the average grain size of the sheet decreased from 11.2 μm to 6.0 μm and 34.2% initial soft texture component (<11–21> //normal direction (ND)) was transformed into the hard texture component (<0001> //transverse direction (TD)). The effect of pre-twinning on deformation mechanisms was systematically investigated by slip trace analysis and activation stress (τ) analysis. Basal slip was the dominant deformation mechanism during the tension of the as-extruded (AE) specimen while pre-twinning promoted the activation of non-basal slip, especially prismatic slip in the PT specimen. The texture transformation and reduced critical resolved shear stress (CRSS) ratio between non-basal slip and basal slip induced by pre-twinning were primarily responsible for the high activity of non-basal slip. The underlying strengthening mechanism and the reason for good ductility were also rationally discussed. The strengthening effect of single grain refinement was relatively lower in the weak-textured Mg–3Y alloy. Texture hardening could effectively improve the effect of fine-grain strengthening. The excellent deformation compatibility between basal slip of parent grains and prismatic slip of twins as well as relatively higher activity of the second-order pyramidal slip was the origin of the good ductility of the PT specimen.

Assessment of slip transfer criteria for prismatic-to-prismatic slip in pure Ti from 3D grain boundary data

Slip transfer and blocking across grain boundaries was studied in a Ti foil with a strong rolling texture deformed in tension. Prior to deformation, the shape of the grains and the orientation of the grain boundaries were quantified through laboratory scale diffraction contrast tomography (LabDCT). Mechanical deformation led to the activation of 〈a〉 prismatic slip, and slip transfer/blocking was assessed in > 300 grain boundaries by means of slip trace analysis and electron backscatter diffraction. A categorical model was employed to accurately assess slip transfer, and the "F1 score" of various slip transfer criteria proposed in the literature was evaluated for the first time from 3D grain boundary information. Remarkably, for the prismatic-dominated slip transfer in the current Ti sample, the results show that the best predictions of slip transfer/blocking are provided by the angle κ, which is directly related to the residual Burgers vector, and by the Luster-Morris parameter m'. In contrast, metrics based on the twist angle θ and on the LRB criterion were not able to predict accurately slip transfer/blocking. Thus, the extensive analysis of the 3D grain boundary data and the novel application of LabDCT was able to help clarify the role of grain boundary orientation on the mechanisms of plastic deformation in polycrystals with strong prismatic-dominated slip.

Statistical investigation of deformation mechanisms in rolled Mg sheet during compression

A statistical investigation of the operating slip/twinning modes and their interactions at grain scale over a large area, containing ~400 grains, was carried out on rolled Mg sheets during room-temperature compression based on EBSD and slip trace analysis. For 10% strain, the slip mode was dominated by basal slip (89%). All the 363 identified twins were tension twins. The concave-up stress−strain curve indicated a twinning-dominated deformation behavior, which was further confirmed by the large twinned area fraction (41%) after the deformation. Most twin variants (79%) followed the Schmid law. The Luster−Morris parameter (m′) did not correlate well to twin transmission. However, most twin transmissions (82%) exhibited larger normalized m (Schmid factor) and m′ values. Additional slip systems were frequently active in the twin domains while not in the parent, which can be explained by Schmid law. Slip transfer across the twin boundaries was also observed. Statistical m analysis revealed that twinning activity was closely related to prismatic slip.

A machine learning study on the fatigue crack path of short crack on an α titanium alloy.

In the present study, a physics-informed neural network model based on Bayesian hyperparameter optimization is proposed for the prediction of short crack growth paths. A large number of cyclic loadings at a lower amplitude were applied to an α titanium sample by an ultrasonic fatigue machine to ensure a sufficient amount of data for machine learning. The grain size, grain orientation and grain boundary direction on the path, as well as crack growth direction, were selected as feature data for training the prediction model. The optimizations of the size ratio and the angle operation were conducted to compare different data processing methods, respectively. After evaluation, eventually, a model for predicting crack growth path is obtained with a reliable performance of 10% tolerance on the path angle at each grain boundary. And the prediction effect of the proposed model is better than that of some classic machine learning models and slip trace analysis. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

The mechanism for Li-addition induced homogeneous deformation in Mg-4.5wt.% Li alloy

The mechanism by which Li additions induce a more homogeneous deformation was systematically investigated in this study by comparing the deformation behavior of pure Mg and Mg-4.5 wt.% Li using experiments, crystal plasticity simulations, and theoretical calculations. The results of the digital image correlation measurements showed that under tension along the transverse direction (TD), strong localized deformation bands with an angle of approximately 20° with respect to the TD were observed in pure Mg, but were absent in Mg-4.5 wt.% Li. Slip trace analyses indicated that basal slip was the predominant deformation mode for pure Mg, whereas that for Mg-4.5 wt.% Li was prismatic slip. A high relative activity of pyramidal 〈c+a〉 slip, approximately 17 %, was observed in Mg-4.5 wt.% Li at a high strain of 10 %. Contraction or double twins were hardly detected during the entire tension process. Crystal plasticity simulations revealed that the 4.5 wt.% Li addition dramatically reduced the critical resolved shear stress (CRSS) ratio of pyramidal 〈c+a〉 slip: prismatic slip: basal slip, which was 31.5:21:1 for pure Mg and 4.3:1.3:1 for Mg-4.5 wt.% Li. Theoretical calculations using the CRSS ratios determined by simulations revealed that easy and uniform deformation propagation induced by a dramatically reduced CRSS ratio of prismatic slip to basal slip played a more important role in improving the deformation homogeneity, in addition to the enhanced activity of pyramidal 〈c+a〉 slip. The mechanisms for how Li additions improve the ductility of Mg are also revisited in this paper.